Oscillation generator circuit



R. H. SIEMENS QSGILLATIQN GENERATOR :CIRCUIT Original File ldarch 30, 1937 May 19, 1942.

2 Sheets-Sheet l :liLt.

I Inventor Budaphli May 19, 1942, R'. H. SIEMENS OSCILLATION GENERATORICIRCUIT Ofiginal Filed March so; 1937 2 Sheets-Shee t 2 l 3rwentor lfmgphas' Patented May 19, 1942 OSC ILLATION GENERATOR CIRCUIT Rudolph H. Siemens, Richmond Hill, N. Y., as-

signor to'Radio Corporation of America, a cornotation of Delaware Original application March 30, 1937, Serial No. 133,753, -now Patent No. 2,192,205, dated March 5, 1940. Divided and this application January 5, 1940, Serial No. 312,479

4 Cl ims. (01. 250-35) The present invention relates to oscillation generator circuits of the two-terminal type. By the expression two-terminal oscillator, as understood in engineering practice, is meant a generator employing only a single tuned circuit whose two terminals are required to be con nected to the generator for producing an operative structure. This application is a division of my United States Patent No. 2,192,205, granted March 5, 1940, on 'an application Serial No. 133,753, filed March 30, 1937.

Heretofore, in oscillator circuits designed to cover various frequency ranges, it has been necessary to switch a plurality of contacts in :order to change from one frequency range'toanother. Such arrangements, besides being relatively ex: pensive and cumbersome, are rather complicated and introduce undesirable energy losses.

The present invention, inter alia, overcomes the foregoing disadvantages and provides a relatively simplified oscillation circuit which requires that only one contact be changed in order to switch from one frequency range to another.

Accordingly, one of the objects of the present invention is to provide a simplified oscillator wherein a minimum of switching 'oftuned cir-' cuits is required for obtaining a number of different frequency ranges.

Another object is to provide a simplified regenerative type of two-terminal. oscillator wherein a vacuum tube isemployed to replace the usual feed-back coil.

A further object is to provide a multi-tuberegenerative oscillator in which direct coupling'is employed between the output electrode of one tube and the input electrode of the succeeding tube, and use is made of this direct coupling to provide bias for said input electrode.

A still further object is to provide a two-terminal oscillation generator which can function efficiently in the ultra high frequency range as well as at lower frequencies.

A feature of the invention resides in the use of an automatic amplitude regulator for providing a constant amplitude of oscillations over a desired range of frequencies.

According'to one embodiment of the invention, the tubes of the oscillator may be operated over substantially linear portions of their respective grid-voltage-grid-current characteristics, thus producing oscillations which are substantially free from undesired harmonics.

Other objects, features and advantages will appear from a reading of the following description, taken in conjunction with the accompanying drawings, wherein Figs. 1 to 4, inclusive, illustrate different embodiments of an. oscillation generator circuit constructed in. accordance with the principles of the present invention. In these figures, like parts areindicate'd'by like reference numerals. a

Referring to Fig. 1 in more detail, there is shown a two-terminal multi-tube high fre' quency oscillator comprising a pair of tubes Ti and T2. Although tubes T1 and T2- are here shown as being of the triode type, it is to be distinctly understood that, if desired, such tubes may have additional electrodes. Vacuum tube T1 includes, among its electrodes, a grid G1, a cathode K1 and an anode P Coupled to the grid G1 and cathode K1 is a tuned oscillatory circuit comprisingan inductance L1 having in shunt therewith a variable condenser C4. A switch .S is provided for enabling, alternatively, the selection of anyone of a plurality of other coils L2, L3 etc., for cooperating' with the condenser C4 forobtaining a change in the frequency range 'of the oscillator. The usual gridleak and condensercombination here shownby the reference numerals R2 and C1 provide the automatic bias for the input electrode G1 ofthe J tube. Conductively coupled to the anode P through a direct current path M is a grid G2 of a vacuum tube Tz whose anode Pz is coupled i 7 backto the input circuit'Lr, 04 through connection N; thus providing a feed-back circuit. The feed-back of energy from the output electrode of tube T2 to the input electrode of tube T1 is in such phase and of such magnitude as to overcome the losses in the circuitand produce oscil-' lations. Putting-it another way, it. may be said that the voltage gain of-"the two tubes T1 and T2 is unity or greater between grid G; of tube T1, and the anode P2 of tube T2. I

Directly connected to the connection M, there 7 is shown a resistance R3 which acts as a load for the anode P1, and simultaneously provides grid bias for thegrid G2. An inductance L4, is arranged in series with R3 and is of such value as to correct for the phase shift occurring in the load circuit R3. A radio frequency by-pass condenser C3 connects the cathodes of the two tubes togetheninthe manner indicated in the drawings. The usual source of potential indicated as 3+ is connected to the lower terminals of coils L1, L2, and L: for maintaining the anodes P1 and P2 of the tubes at a positive potential relative to their respective cathodes, The path of the .positive source 3+ for the ,anodes of the -tubes may be tracedthrough-resistance R1, through inductance L1, switch S, and feed-back path N to the anode P2. The positive polarizing potential for the anode P1 is obtained through tube T2, over the cathode K2 and its connection to the lower terminal of inductance L4, and resistance R3. It will be obvious that there will be a difference in the magnitude of the polarizing potentials applied to the anodes P1 and P2 due mainly to the voltage drop in the tube T2. actually used in practice, the voltage available from the source 3+ was 250 volts. The magni tude of the voltage applied to the anode P1 was less than that applied to the anode of tube T2, with respect to ground or the negative terminal of the anode supply, the difference varying in accordance with the amount of grid bias on the electrodes of the tubes. A radio frequency bypass and blocking condenser C2 is connected between the anode source B+ and the cathode of the tube T1 for preventing a direct path for the current from the positive source 3+ to ground. Condenser G2 also completes the tuned circuit between the lower end of C1 and inductances L1, L2, and L3. This condenser 02 in conjunction with resistor R1 forms a filter isolating the oscillator circuit from other circuits which may be connected to the same power sup-ply system.

The operation of the circuit is as follows. Any

voltage appearing across the tuned circuit L1, C1

is impressed across the grid G1 andthe cathode K1 of the tube T1, whereupon it developes a voltage on the anode P1 substantially 180 out of phase with the original voltage. The oppositely phased voltage is then transmitted to the grid G2 by the connection M. The tube T2 functions Fig. 2 illustrates the same circuit arrangement as that shown in Fig. 1, the electrodes of both tubes being contained within a single envelope. Since the connections of Fig. 2 are similar in every respect with those of Fig. 1, and the operation of the oscillator is the same, it is not believed necessary to repeat what has been said before. In one oscillator actually constructed in accordance with the circuit of Fig. 2, there was used an RCA type 608 dual triode. With such a tube, oscillations as high as 38 megacycles were obtained. This frequency is given by way of example, merely to indicate the possibilities of the circuit, but it does not representthe limit to which the oscillator of the invention can be operated.

In the dual tube where a common cathode is employed for the two grids and their respective anodes, such as in the RCA type 6N7, a circuit such as shown in Fig. 3 may be used instead of that shown in Fig. 2. Besides using a common cathode, Fig. 3 differs from Fig. 2 mainly in the use of a bucking battery F inserted in the lead M, the battery being so polarized as to provide the correct operating bias for the grid shown in the upper section of the envelope of the tube. An additional source of anode supply B'+ is employed to supply potential to the anode of the lower portion of the tube, which anode corresponds to P1 of Fig. 1. The reason why another anode battery is required for P1 in this instance In one embodiment is because the electron paths are no longer in series as is the case in Figs. 1 and 2. The buckwith that of Figs. 1 and 2.

Fig. 4 illustrates another embodiment of an oscillationgenerator in accordance with the principles of the present invention. The operation of this circuit is substantially the same as that of the other figures with the addition of an automatic amplitude regulator feature described hereinafter. The oscillator of this feature employs a single electron discharge device of the ,Radiotron type 6F? consisting of a combination triode and variable mu pentode, although it will be appreciated that, if desired, two separate tubes may be employed. The automatic amplitude regulator feature consists of a connection from the grid G1 of the triode portion of the tube to the grid G '2 of the pentode portion. This connection includes a resistance-condenser filter network R7, Cs and a resistor R5. The pentode screen grid portion of the tube is used in order to obtain' a wide range of control of the voltage amplification in this portion of the circuit, be-

plied with a suitable positive potential from asource of supply B". The condenser C7 serves to isolate the anode P1 from the grid Gz for direct current. 1

The automatic amplitude regulator feature functions as follows: Assuming that the oscillation generator is generating oscillations of a certain amplitude, then a voltage will appear across the resistance R2 due to the current drawn by the gridG1. This voltage will be polarized negatively with respect to the cathode K, and will charge a condenserce to the peak value of this negativevolta'ge through the resistor R7. This voltage appearing on condenser C6 is then passed onto the grid G'z sothat the potential appearing on this last grid is essentially the same as that on the grid G1. This amount of potential on the grid G52 will allow the tube to function with a certain voltage amplification. If the oscillator now tends to oscillate morestrongly, a larger potential .will be developed across the resistance R2 which, in turn, is passed to the condenser 06 charging it more negatively than before, and thus a more negative potential will in turn be passed on 'to' grid G2. Because of the action of the variable mu pentode portion of the tube, the gain of this portion of the circuit will be reduced from that formerly obtained when the oscillation generator was generating voltage of lower amplitude, thus lowering the amount of feed-back voltage transferred from the'anode' P'z back over connection N to the grid G1. This lowered feed-back potential will then result in a lower amplitude of oscillations which will be similar to that initially started in the circuit. Conversely, if the amplitude falls below the original assumed level, the gainofthe pentode portion of the tube is increased, thus restoring the voltage amplitude of the energy on grid G1 to the predetermined level. In this way, the oscillation generator functions to produce a constant amplitude of oscillations as the losses of the circuit vary.

it is only necessary to move the single pole switch S to engage a single contact, in order to select any desired frequency range which maybe characteristic of a particular coil L1, L2, or L3. This is possible because one terminal of each of these coils is permanently connected to the circuit while the other terminal is connected to a contact of the switching mechanism S.

Although the invention has been described with particular reference to circuits-employing two separate electron discharge device paths, either in separate envelopes or combined in a single envelope, it is to be distinctly understood that the invention is not limited to such particular arrangements since, if desired, any even multiple of two electron discharge device paths may be employed.

What is claimed is:

l. A system for the generation of high frequency oscillations comprising first and second electron discharge paths, each path having an anode, a grid, and electron emitting means, a connection from the anode of said first path to the grid of said second path, and a feed-back circuit from the anode of said second path to the grid of said first path, means for applying a suitable bias to each of said grids and means for applying polarizing potentials to said anodes to cause the flow of current through said electron discharge paths, a condenser connected between one of said grids and said electron emitting means, a plurality of inductance coils of different values each having a terminal permanently connected electrically to one electrode of said condenser and another terminal to a contact, a switch connected to the other electrode of said condenser and adapted to engage any one of said contacts for selectively coupling any one of said inductance coils in parallel relation to said condenser, whereby said system may generate oscillations of a frequency range determined by said condenser and the selected coil, and an automatic amplitude regulator constituted as a filter network and comprising a resistive connection from the grid of said first electron discharge path to the grid of said second electron discharge path, and a shunt capacitor connected between said electron emitting means and an intermediate point on said resistive connection.

2. An oscillation generator comprising first and second electron space discharge paths, said first path including electron emitting means, a grid and an anode, said second path including electron emitting means, first and second grids and an anode; said second path having a variable mu characteristic, a connection between the electron emitting means of said two paths, a resistance connected between the grid of said first path and said electron emitting means an alternating current connection including a series arnetwork connected between the grid of said first path, said electron emitting means and the first grid of said second path, connections from both of said anodes and from said second grid to suitable sources of positive polarizing potentials,

said condenser serving to isolate the anode of said first path from the first grid of said second path for direct current.

3. An oscillation generator comprising a discharge tube of the triode-pentode type wherein the triode discharge path extends from a common cathode through a grid to an anode, and the pentode discharge path extends from said common cathode through a control grid, a screen grid and a suppressor grid to a second anode, said suppressor grid being connected to said common cathode, a grid resistor connected between the triode grid and the cathode, a capacitor connected between the triode anode and the control grid of the pentode path, a second capacitor connected between the pentode anode and the triode grid, a parallel tuned circuit coupled through connections of low impedance to energy of the operation frequency between the triode grid and the cathode, a T-filter network constituted as a series resistance and shunt capacitance Where the resistance is connected between the triode grid and the pentode control grid and the capacitance is connected to said cathode, and operating potential sources applied between the cathode, the pentode screen grid andboth anodes. f

4. A system for. the generation of high frequency oscillations comprising a vacuum tube having within a single evacuated envelope, first and second space discharge paths each having an anode and a gridya common cathode for said space discharge paths; a connection from the anode of one path to the grid of the other path; and a feed-back connection from the other anode to the other grid; a parallel tuned circuit coupled through connections of low impedance to energy of the operating frequency between-one of said grids and said cathode; means for applying a suitable bias to each of said grids; means for applying suitable polarizing potentials to said anodes; and an automatic amplitude regulator comprising a direct current connection between said two grids, said last connection including a resistor network and a condenser connecting a point on said network and said cathode.

RUDOLPH H. SIEMENS. 

